Engine starting apparatus

ABSTRACT

When starting an engine, it is judged whether a catalyst is in an inactive condition or not and, if it is judged that the catalyst is in an inactive condition, the motor field current is reduced to control the output characteristic of the starter to a high-speed type, thus enabling the engine to be driven at high speed. As the engine rpm during driving rises compared with the normal case (the case where the catalyst is in an active condition), the amount of fuel remaining in the intake port and the cylinder decreases, and the injected fuel properly contributes to combustion. Accordingly, even when the catalyst is in an inactive condition, emissions (of HC) emitted into the atmosphere can be reduced.

FIELD OF THE INVENTION

[0001] The present invention relates to an engine starting apparatus forstarting an engine at high speed (rpm) when a catalyst is in an inactivecondition.

BACKGROUND OF INVENTION

[0002] Traditionally, series-wound DC motors, in which a field coil isconnected in series with an armature coil, have often been employed asstarter motors in engine starting apparatuses (refer to JapaneseUnexamined Patent Publication No. 2000-125579). The output of this typeof DC motor is determined based on the engine cranking torque, thelowest rotational speed capable of starting the engine, etc. so that asufficient rotational speed can be obtained even in the wintertime(under extremely low temperature conditions).

[0003] However, when the engine is being started by the DC motor, as theengine starting speed (cranking rpm) is low, and the pressure of intakeair being drawn into the cylinder is therefore low, fuel is notsufficiently atomized and the amount of fuel remaining in the intakeport increases. Furthermore, at a low engine speed, the cylinderpressure is low even when compressed by the piston, and the amount ofunatomized fuel remaining in the cylinder also increases.

[0004] As the engine speed increases thereafter, part of the remainingfuel is used for combustion, but as the air/fuel ratio becomes rich,much of the remaining fuel is exhausted as unburned gas. In particular,when a catalyst is in an inactive condition, such as when the engine isstarted from a cold condition, the remaining fuel may be emitteddirectly into the atmosphere because the purification performance of thecatalyst is low.

[0005] One possible approach to reducing the amount of remaining fuelwould be to reduce the amount of fuel injection, but the amount of theremaining fuel is difficult to predict; therefore, if the amount of fuelinjection is simply reduced, the engine starting performance may fall,depending on the properties of the fuel.

[0006] The present invention has been devised in view of the abovesituation, and an object of the invention is to provide an enginestarting apparatus that can reduce emissions (HC) emitted into theatmosphere even when the catalyst is in an inactive condition.

SUMMARY OF INVENTION

[0007] (First Aspect of the Invention)

[0008] An engine starting apparatus using at least a starter accordingto a first aspect of the invention comprises catalyst condition judgingmeans for judging whether a catalyst for purifying exhaust gas in theengine is in an inactive condition or not and, when the engine is beingstarted, if the catalyst is judged to be in an inactive condition, theengine is started at higher speed than when the catalyst is in an activecondition.

[0009] When the catalyst is in an inactive condition, if the engine isstarted at high speed, the engine speed increases compared with that inthe normal condition (that is, when the catalyst is in an activecondition); as a result, the amount of fuel remaining in the intake portand the cylinder decreases, and the injected fuel properly contributesto combustion. Accordingly, even when the catalyst is in an inactivecondition, emissions (HC) emitted into the atmosphere can be reduced.

[0010] (Second Aspect of the Invention)

[0011] An engine starting apparatus according to a second aspect of theinvention has a first starter having a high torque type outputcharacteristic and a second starter having a high speed type outputcharacteristic, and when starting the engine, if the catalyst is judgedto be in an inactive condition, the engine is started by using thesecond starter.

[0012] When the catalyst is in an inactive condition, if the engine isstarted at high speed by using the second starter, the engine speedincreases compared with that in the normal condition (that is, when thecatalyst is in an active condition); as a result, the amount of fuelremaining in the intake port and the cylinder decreases, and theinjected fuel properly contributes to combustion. Accordingly, even whenthe catalyst is in an inactive condition, the emissions emitted into theatmosphere can be reduced.

[0013] (Third Aspect of the Invention)

[0014] In the engine starting apparatus, the catalyst condition judgingmeans judges that the catalyst is in an inactive condition when thetemperature of the catalyst is lower than a predetermined temperature.

[0015] In this case, the catalyst can be reliably judged to be in aninactive condition because the condition of the catalyst (activecondition/inactive condition) is judged based on the temperature of thecatalyst itself. Accordingly, when the temperature of the catalyst islower than the predetermined temperature, it is judged that the catalystis in an inactive condition, and the emissions can be reduced bystarting the engine at higher speed than when the catalyst is in anactive condition.

[0016] (Fourth Aspect of the Invention)

[0017] In the engine starting apparatus, the catalyst condition judgingmeans judges that the catalyst is in an inactive condition when oiltemperature or coolant temperature of the engine is lower than a firstpredetermined temperature.

[0018] When the oil temperature or coolant temperature of the engine islow (lower than the first predetermined temperature), it is judged thatthe temperature of the catalyst is also low; therefore, in this case, itis judged that the catalyst is in an inactive condition, and theemissions can be reduced by cranking the engine at higher speed thanwhen the catalyst is in an active condition.

[0019] (Fifth Aspect of the Invention)

[0020] In the engine starting apparatus, the catalyst condition judgingmeans judges that the catalyst is in an inactive condition when theengine has been in a stopped condition for more than a predeterminedlength of time.

[0021] When the time elapsed from the time that the engine was laststopped is long (longer than a predetermined length of time), it isjudged that the temperature of the catalyst is low; therefore, in thiscase, it is judged that the catalyst is in an inactive condition, andthe emissions can be reduced by starting the engine at higher speed thanwhen the catalyst is in an active condition.

[0022] (Sixth Aspect of the Invention)

[0023] The engine starting apparatus is used in an engine automaticstopping/starting system which automatically controls the stopping andrestarting of the engine, and its catalyst condition judging meansjudges that the catalyst is in an inactive condition when the engine isstarted by operating an ignition key but not when the engine isrestarted by the engine automatic stopping/starting system.

[0024] In the system that automatically controls the stopping andrestarting of the engine, it is judged that the catalyst is in an activecondition when the engine is restarted (by automatic control). On theother hand, when the driver starts the engine by operating the ignitionkey, it is judged that the catalyst is in an inactive condition;therefore, in this case (when the engine is started by operating theignition key), it is judged that the catalyst is in an inactivecondition, and the emissions can be reduced by driving the engine athigher speed than when the catalyst is in an active condition.

[0025] (Seventh Aspect of the Invention)

[0026] The engine starting apparatus includes motor control means forcontrolling an output characteristic of a motor provided in the starter,and the motor control means changes the output characteristic of themotor to a high speed type, thereby allowing the engine to be driven athigh speed.

[0027] When the engine is driven at high speed by changing the outputcharacteristic (torque-rpm) of the motor to the high-speed-type, theengine speed increases compared with that in the normal condition, andthus the emissions can be reduced.

[0028] (Eighth Aspect of the Invention)

[0029] In the engine starting apparatus, the motor control meanscontrols the output characteristic of the motor to the high speed typeby changing the field current of the motor.

[0030] As the output characteristic of the motor can be controlled basedon the field current of the motor, the engine can be cranked at highspeed by performing control to change the field current, therebyswitching the output characteristic of the motor to the high speed type.

[0031] (Ninth Aspect of the Invention)

[0032] In the engine starting apparatus, the motor has a series coil anda shunt coil, and the motor control means comprises an energizationcircuit which can energize the shunt coil in such a manner that thefield current flowing in the shunt coil is opposite in direction to thefield current flowing in the series coil, wherein the motor controlmeans reduces the field current of the motor by controlling through theenergization circuit at least either the amount of the current or thedirection of the current flowing in the shunt coil.

[0033] If the field current of the shunt coil is reduced, sufficientlyhigh engine speed may not be achieved because of the influence of themagnetic flux produced in the series coil. In this case, by energizingthe shunt coil in such a manner that the field current flowing in theshunt coil is opposite in direction to the field current flowing in theseries coil, the influence of the magnetic flux produced in the seriescoil can be cancelled out, and a sufficiently high engine speed can beachieved. As a result, the engine can be driven at high speed.

[0034] (10th Aspect of the Invention)

[0035] In the engine starting apparatus, the motor control meansincludes a field current reducing means capable of reducing the fieldcurrent flowing in a field coil (series coil) of the motor, and themotor control means reduces the field current of the motor by using thefield current reducing means.

[0036] By using the field current reducing means to reduce the fieldcurrent flowing in the field coil (series coil) of the motor, the outputcharacteristic of the motor can be controlled to the high speed type, sothat the engine can be started at high speed.

[0037] (11th Aspect of the Invention)

[0038] In the engine starting apparatus, the motor control means reducesthe field current of the motor in accordance with speed of the engine orthe starter.

[0039] As the field current is controlled in accordance with the speedof the engine or the starter, the engine can be driven properly at highspeed.

[0040] (12th Aspect of the Invention)

[0041] In the engine starting apparatus, the motor control means reducesthe field current of the motor in accordance with a crankshaft positionin the engine.

[0042] As the field current is controlled in accordance with the enginecrankshaft position, the engine can be driven more properly at highspeed by suppressing the effects of the torque/rpm variations associatedwith the piston intake-compression-expansion-exhaust strokes.

[0043] (13th Aspect of the Invention)

[0044] In the engine starting apparatus, the motor control means reducesthe field current of the motor after a piston reaches the top deadcenter in any one of cylinders after the starting of the engine.

[0045] After the starting of the engine, air substantially atatmospheric pressure continues to be compressed in the engine untilafter a piston reaches the top dead center in any one of the cylinders;therefore, during this period, large torque is required to start theengine.

[0046] However, once a piston reaches the top dead center in any one ofthe cylinders, the engine itself generates driving force because of theexpansion that follows the compression, and the large torque for drivingthe engine is no longer necessary. In view of this, before a pistonreaches the top dead center in any one of the cylinders, an increase inthe field current switches the output characteristic of the starter tothe high torque type, and then, after a piston reaches the top deadcenter is reached in any one of the cylinders, a reduction in the fieldcurrent switches the output characteristic of the starter to the highspeed type so that the engine can be properly driven at high speed.

[0047] (14th Aspect of the Invention)

[0048] In the engine starting apparatus, the motor control means sets anelectric current value that maximizes the output of the motor as acontrol target value for the field current.

[0049] If the output of the motor can be maximized by controlling thefield current, the engine can be started at maximum speed, and hence,the emission reducing effect can be maximized.

[0050] (15th Aspect of the Invention)

[0051] In the engine starting apparatus according to any one of theeighth to 14th aspects, the motor control means stops the field currentreducing control when the oil temperature or the coolant temperature ofthe engine is lower than a second predetermined temperature which islower than the first predetermined temperature for judging whether thecatalyst is in an inactive condition or not.

[0052] At extremely low temperatures, the viscosity of the engine oilincreases, and higher engine torque may be required when starting theengine. Accordingly, when the oil temperature or coolant temperature ofthe engine is lower than the predetermined temperature (secondpredetermined temperature) below which higher engine torque is required,the field current reducing control is stopped, and the motor is drivenwith a high torque type characteristic so that the engine can be startedproperly even at extremely low temperatures.

[0053] (16th Aspect of the Invention)

[0054] In the engine starting apparatus, the motor control means stopsreducing the field current when oil temperature or coolant temperatureof the engine is higher than a third predetermined temperature which ishigher than the first predetermined temperature for judging whether thecatalyst is in an inactive condition or not.

[0055] In high temperature conditions, such as when the engine isstopped after heavy load driving such as uphill driving, and the engineis restarted immediately after that, the cylinder is sealed moretightly, requiring higher engine torque when starting the engine.Accordingly, when the oil temperature or coolant temperature of theengine is higher than the predetermined temperature (third predeterminedtemperature) above which higher engine torque is required, it is stoppedto reduce the field current, and the motor is driven with a high torquetype characteristic so that the engine can be started properly even atextremely high temperatures.

[0056] (17th Aspect of the Invention)

[0057] In the engine starting apparatus, the motor control means stopsreducing the field current when the speed of the engine or the starterhas failed to reach a predetermined speed.

[0058] When the engine is driven at high speed by reducing the fieldcurrent of the motor, if the engine speed does not rise for some reason,reduction of the field current is stopped, and the motor is driven witha high torque type characteristic so that the engine can be properlyeven in a faulty condition.

[0059] (18th Aspect of the Invention)

[0060] In the engine starting apparatus, the motor control means stopsreducing the field current when the battery is at low state of charge.

[0061] When the battery is at low state of charge, such as when thevehicle has been left standing for an extended period of time, theoutput of the starter drops. Accordingly, when the battery is at lowstate of charge, the field current is not reduced, and the motor isdriven with a high torque type characteristic so that the engine can bedriven properly.

[0062] (19th Aspect of the Invention)

[0063] In the engine starting apparatus, a power supply means forsupplying field current to the shunt coil is provided separately from abattery, and the motor control means stops reducing the field currentwhen the power supply means is at lower stage of charge than apredetermined level.

[0064] A separate power supply (for example, a capacitor) may beprovided to energize the field coil (shunt coil) in order to prevent thebattery voltage from dropping due to a large current flow to the motorwhen controlling the field current of the motor. Here, if the separatepower supply (power supply means) is at lower state of charge than thepredetermined battery charge level, the magnetic field necessary fordriving the motor cannot be formed; in that case, the field current forthe shunt coil is not reduced so that the engine can be driven properly.

[0065] (20th Aspect of the Invention)

[0066] In the engine starting apparatus, the motor provided in thestarter is a DC motor.

[0067] By using a DC motor, the system of the present invention can beimplemented in a simple manner and at low cost.

[0068] (21st Aspect of the Invention)

[0069] In the engine starting apparatus, the engine is started by usingthe first starter when the oil temperature or the coolant temperature ofthe engine is lower than a second predetermined temperature which islower than the first predetermined temperature for judging whether thecatalyst is in an inactive condition or not.

[0070] At extremely low temperatures, the viscosity of the engine oilincreases, and higher engine torque may be required when starting theengine. Accordingly, when the oil temperature or coolant temperature ofthe engine is lower than the predetermined temperature (secondpredetermined temperature) below which higher engine torque is required,the second starter having the high speed type output characteristic isnot used, but the first starter having the high torque type outputcharacteristic is switched in to start the engine; by so doing, theengine can be started properly even at extremely low temperatures.

[0071] (22nd Aspect of the Invention)

[0072] In the engine starting apparatus, the engine is started by usingthe first starter when the oil temperature or the coolant temperature ofthe engine is higher than a third predetermined temperature which ishigher than the first predetermined temperature for judging whether thecatalyst is in an inactive condition or not.

[0073] In high temperature conditions, such as when the engine isstopped after heavy load driving such as uphill driving, and the engineis restarted immediately, the cylinder is sealed more tightly, requiringhigher engine torque when starting the engine. Accordingly, when the oiltemperature or coolant temperature of the engine is higher than thepredetermined temperature (third predetermined temperature) above whichhigher engine torque is required, the second starter having the highspeed type output characteristic is not used, but the first starterhaving the high torque type output characteristic is switched in tostart the engine; by so doing, the engine can be started properly evenat extremely low temperatures.

[0074] (23rd Aspect of the Invention)

[0075] In the engine starting apparatus, when the engine was started byusing the second starter, if the speed of the engine or the secondstarter failed to reach a predetermined speed, the engine is started byswitching from the second starter to the first starter.

[0076] When the engine is started by using the second starter having thehigh speed type output characteristic, if the engine rpm does not risefor some fault, the second starter is stopped, and the first starterhaving the high torque type output characteristic is switched in tostart the engine; by so doing, the engine can be started properly evenin a faulty condition.

[0077] (24th Aspect of the Invention)

[0078] In the engine starting apparatus, the engine is started by usingthe first starter when a battery is at low stage of charge.

[0079] When state of charge the battery is at low stage of charge, suchas when the vehicle has been left standing for an extended period oftime, the second starter having the high speed type outputcharacteristic is not used, but the first starter having the high torquetype output characteristic is switched in to start the engine; by sodoing, the engine can be started properly.

[0080] (25th Aspect of the Invention)

[0081] In the engine starting apparatus, when the engine speed is higherthan a predetermined speed, the amount of fuel injection is reducedcompared with a case where the catalyst is in an active condition.

[0082] When the engine speed is higher than the predetermined speed, theair/fuel ratio for combustion becomes rich, because the amount of fuelremaining in the intake port and the cylinder decreases; therefore, ifthe same amount of fuel as that in the case of normal engine starting(engine starting when the catalyst is in an active condition) isinjected, unburned gas will be emitted. Accordingly, by reducing theamount of fuel injection compared with that of the normal case, theamount of unburned gas emitted can be reduced, and the emissions canthus be reduced.

[0083] (26th Aspect of the Invention)

[0084] In the engine starting apparatus, when the speed of the engine ishigher than the predetermined speed, the amount of fuel injection isreduced depending on air/fuel ratio.

[0085] By reducing the amount of fuel injection depending on air/fuelratio, the emissions can be further reduced.

[0086] (27th Aspect of the Invention)

[0087] In the engine starting apparatus, fuel injection is started afterit is detected that intake manifold pressure in the engine is lower thana predetermined value.

[0088] If the engine intake manifold pressure is high, the fuel is notsufficiently atomized and the air/fuel mixture in the intake port cannotbe properly introduced into the cylinder. Therefore, by starting thefuel injection after detecting that the engine intake manifold pressureis lower than the predetermined value, the amount of unburned gas in theintake port can be reduced, which contributes to reducing the emissions.

[0089] (28th Aspect of the Invention)

[0090] In the engine starting apparatus, fuel injection is started afterit is detected that the number of revolutions of the engine is higherthan a predetermined speed.

[0091] If the engine speed is higher than the predetermined speed, theair/fuel mixture in the intake port can be properly introduced into thecylinder, and the emissions can thus be reduced.

[0092] (29th Aspect of the Invention)

[0093] In the engine starting apparatus, fuel injection is started afterit is detected that the total rpm of the engine counted from thestarting of the engine has reached a predetermined value.

[0094] If the total rpm of the engine counted from the starting of theengine is larger than the predetermined value, it is expected that theintake manifold pressure is sufficiently low; therefore, the air/fuelmixture in the intake port can be properly introduced into the cylinder,and the emissions can thus be reduced.

[0095] (30th Aspect of the Invention)

[0096] In the engine starting apparatus, fuel injection is started afterit is detected that a predetermined time has elapsed from the startingof the engine.

[0097] If the predetermined time has elapsed from the starting of theengine, it is expected that the intake manifold pressure is sufficientlylow; therefore, the air/fuel mixture in the intake port can be properlyintroduced into the cylinder, and the emissions can thus be reduced.

[0098] (31st Aspect of the Invention)

[0099] In the engine starting apparatus, when starting the engine bydriving the engine at high speed, a threshold speed for perfectcombustion is changed according to the engine speed.

[0100] When the engine is started at high speed, the engine may continueto be driven beyond the threshold speed for perfect combustion which isused in normal engine starting (engine starting when the catalyst is inan active condition). In view of this, when starting the engine bydriving it at high speed, the threshold speed for perfect combustion ischanged according to the engine speed; this ensures proper starting ofthe engine.

[0101] (32nd Aspect of the Invention)

[0102] In the engine starting apparatus, when the engine speed hasreached the threshold speed for perfect combustion, operation of thestarter is stopped.

[0103] In the case of a system that automatically starts the starter ofthe present invention, the engine can be started properly if the drivingby the starter is stopped when the engine speed has reached thethreshold speed for perfect combustion.

[0104] Other features and advantages will become apparent in discussionof the embodiments of the invention in relation to the followingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

[0105]FIG. 1 is an electrical circuit diagram of an engine startingapparatus.

[0106]FIG. 2 is a diagram showing starter output characteristics.

[0107]FIG. 3 is a flowchart illustrating the operation of the enginestarting apparatus (first embodiment).

[0108]FIG. 4 is a time chart for explaining the operation and effect (HCreduction) of the embodiment.

[0109]FIG. 5 is a flowchart illustrating the operation of the enginestarting apparatus (second embodiment).

[0110]FIG. 6 is a flowchart illustrating the operation of the enginestarting apparatus (third embodiment).

[0111]FIG. 7 is an electrical circuit diagram of an engine startingapparatus (third embodiment).

[0112]FIG. 8 is an electrical circuit diagram of an engine startingapparatus (fourth embodiment).

EMBODIMENTS OF INVENTION

[0113] Embodiments of the present invention will be described below withreference to the drawings.

[0114] (Embodiment 1)

[0115]FIG. 1 is an electrical circuit diagram of an engine startingapparatus.

[0116] The engine starting apparatus A of this embodiment is used in theso-called idle stop system which automatically stops the engine when thevehicle comes to a stop, for example, at an intersection or in trafficjam, and restarts the engine (not shown) when a prescribed startingcondition is satisfied (for example, when the driver releases the brakepedal and steps on the accelerator pedal); the engine starting apparatusis equipped with a starter 1 for starting the engine and is controlledby an Electronic Control Unit (ECU) 2 (which contains motor controlmeans of the present invention).

[0117] The starter 1 comprises a compound-wound DC motor, the rotationaloutput of which is transmitted to the engine to start the engine. Thestarter 1 may be of a gear drive type which brings the pinion gear intoengagement with the engine ring gear, or of a belt drive type whichtransmits the output of the starter 1 to the engine by means of a drivebelt.

[0118] The DC motor has a series coil 4 connected in series with anarmature 3, and a shunt coil 6 connected to an energization circuit 5described below, and is energized by being connected to a vehiclebattery 10 via a starter relay 8 and an electromagnetic switch 9 when anignition key 7 is turned on (to position ST).

[0119] The energization circuit 5 comprises four control elements 11(for example, MOS-FETs) connected in the form of a bridge, whose oneinput terminal 5 a is connected to the positive terminal of the vehiclebattery 10 via the electromagnetic switch 9, and whose other inputterminal 5 b is grounded.

[0120] The ECU 2 controls the field current flowing in the shunt coil 6by controlling the energization circuit 5. More specifically, the ECU 2controls the amount and direction of the current flowing in the shuntcoil 6 (the current can be made to flow in the direction opposite to thedirection of the current in the series coil 4) in accordance with theduty cycle of each control element 11 in the energization circuit 5. Asa result, as shown in FIG. 2, the output characteristic of the DC motorbecomes a higher speed type as the field current decreases, and a highertorque type as the field current increases.

[0121] Next, the operation of the engine starting apparatus A will bedescribed with reference to the flowchart shown in FIG. 3.

[0122] Step 10: Presence or absence of a start request is checked. Here,when a restart request is detected after automatic stopping of theengine, it is decided that a start request has occurred. If the resultof the decision is YES, the process proceeds to the next step 20, but ifthe result of the decision is NO, the process is terminated.

[0123] Step 20: Decision is made as to whether the catalyst forpurifying the exhaust gas is in an inactive condition or not. Theinactive condition of the catalyst is detected based on the followingcriteria.

[0124] a) The catalyst temperature is lower than a predeterminedtemperature (for example, 300° C.).

[0125] b) The oil temperature or coolant temperature of the engine islower than a first predetermined temperature (for example, 60° C.).

[0126] c) The engine has been in a stopped condition for more than apredetermined length of time (for example, 10 minutes).

[0127] If the result of the decision is NO, the process proceeds to thenext step 30, but if the result of the decision is YES, the processproceeds to step 60.

[0128] Step 30: Duty cycle of each control element 11 in theenergization circuit 5 is controlled (increased) so as to increase thefield current flowing in the shunt coil 6.

[0129] Step 40: Starter 1 is turned on.

[0130] Step 50: After performing normal engine control, the processproceeds to step 140.

[0131] Step 60: Duty cycle of each control element 11 in theenergization circuit 5 is controlled (increased) so as to increase thefield current flowing in the shunt coil 6.

[0132] Step 70: Starter 1 is turned on.

[0133] Step 80: Decision is made as to whether top dead center isdetected in any one of the cylinders. If top dead center is detected(the result of the decision is YES), the process proceeds to step 90.

[0134] Step 90: Duty cycle of each control element 11 in theenergization circuit 5 is controlled (decreased) so as to reduce thefield current flowing in the shunt coil 6. In this case, the duty cycleof each control element 11 may be decreased gradually in order toprevent shock that may be caused due to an abrupt change in the outputcharacteristic of the starter 1.

[0135] Step 100: Decision is made as to whether the engine rpm hasexceeded a predetermined rpm N. Here, whether the engine rpm hasincreased up to the rpm at which fuel injection can be started isdetermined by reference to the predetermined rpm N. When the engine rpmhas exceeded the predetermined rpm N (the result of the decision isYES), the process proceeds to step 110.

[0136] Step 110: The amount of fuel injection is reduced compared withthat in normal engine control. More specifically, the amount of fuelinjection is determined from the current engine rpm by referring to amap. In Step 110, the amount of fuel injection may be controlled basedon the air/fuel ratio.

[0137] Step 120: Fuel injection to engine is started.

[0138] Step 130: Threshold rpm S for perfect combustion is determinedfrom the current engine rpm by referring to a map.

[0139] Step 140: Decision step 140 is repeated until the current enginerpm exceeds the threshold rpm S for perfect combustion determined instep 130. When the threshold rpm S for perfect combustion is exceeded(the result of the decision is YES), the process proceeds to step 150.

[0140] Step 150: Starter 1 is turned off, whereupon the process isterminated.

[0141] (Effect of Embodiment 1)

[0142] According to the present embodiment, when the catalyst is in aninactive condition, first, the engine is driven by controlling theoutput characteristic of the starter 1 to the high torque type (byincreasing the field current), as shown in FIG. 4(a), and then, aftertop dead center is reached in any one of the cylinders, the outputcharacteristic of the starter 1 is controlled to the high speed type byreducing the field current of the motor, thereby making it possible toproperly drive the engine at high speed. As a result, as the engine rpmduring cranking rises compared with the normal case (the case where thecatalyst is in an active condition), as shown in FIG. 4(b), the amountof fuel remaining in the intake port and the cylinder decreases, and theinjected fuel properly contributes to combustion. Accordingly, even whenthe catalyst is in an inactive condition (the purification performanceis low), emissions (HC) emitted into the atmosphere can be reduced (seeFIG. 4(c)).

[0143] Further, when the engine rpm is higher than the predetermined rpmN, the air/fuel ratio for combustion becomes rich, because the amount offuel remaining in the intake port and the cylinder decreases; therefore,if the same amount of fuel as that in the case of normal engine starting(engine starting when the catalyst is in an active condition) isinjected, unburned gas will be emitted. Accordingly, by reducing theamount of fuel injection compared with the case of normal enginecontrol, the amount of unburned gas emitted can be reduced, whichcontributes to further reducing the emissions.

[0144] The first embodiment has been described by assuming the casewhere the engine is restarted after automatic stopping but, even whenstarting the engine by activating the starter 1 through operation of theignition key 7, the same effect as achieved in the first embodiment canbe obtained by reducing the field current of the motor and therebydriving the engine at high speed when the catalyst has been judged to bein an inactive condition. In this case, besides the previously givencriteria a) to c) for judging the inactive condition of the catalyst, itmay be judged that the catalyst is in an inactive condition when theengine is started by operating the ignition key 7.

[0145] (Embodiment 2)

[0146]FIG. 5 is a flowchart illustrating the operation of the enginestarting apparatus A.

[0147] In this embodiment, steps 80/90 and 100A are performed instead ofthe steps 80 to 100 shown in the flowchart described in the firstembodiment. Otherwise, the process (steps 10 to 70 and 110 to 150) isthe same as that of the first embodiment (the description will not berepeated here).

[0148] Details of the steps 80/90 and 100A will be described below.

[0149] Step 80/90: The field current of the motor is reduced comparedwith the normal case (the case where the catalyst is in a normalcondition). More specifically, the field current is determined from thecurrent engine rpm or starter rpm by referring to a map.

[0150] Step 100A: Decision is made as to whether or not intake manifoldpressure is either equal to or higher than a predetermined value p. Ifthe intake manifold pressure is higher than the predetermined value p(the result of the decision is NO), the process returns to step 80/90,but if the intake manifold pressure is not higher than the predeterminedvalue p (the result of the decision is YES), the process proceeds tostep 110.

[0151] According to the present embodiment, as the field current isreduced according to the rpm of the engine or the starter 1, the enginecan be properly cranked at high rpm.

[0152] Furthermore, as fuel injection starts after detecting that theengine intake manifold pressure is not higher than the predeterminedvalue p, the air/fuel mixture in the intake port can be properlyintroduced into the cylinder, reducing the amount of unburned gas in theintake port; this contributes to reducing the emissions more reliably.

[0153] In the present embodiment, a decision is made in step 100A as towhether the intake manifold pressure is not higher than thepredetermined value p, but instead, decision may be made as to whetherthe total number of revolutions counted from the starting of the enginehas reached a predetermined value in order to start the fuel injectionafter the predetermined value has been reached. Alternatively, adecision may be made as to whether a predetermined time has elapsed fromthe starting of the engine in order to start the fuel injection afterthe predetermined time has elapsed.

[0154] In these cases, as it is judged that the intake manifold pressureis sufficiently low, the air/fuel mixture in the intake port can beproperly introduced into the cylinder, and thus, the emissions can bereduced.

[0155] (Embodiment 3)

[0156]FIG. 6 is a flowchart illustrating the operation of the enginestarting apparatus A.

[0157] This embodiment concerns an example, in which control of thereduction of the field current is stopped and is changed to the normalengine control.

[0158] The details of the control according to this embodiment will bedescribed below with reference to the flowchart.

[0159] Steps 10 to 70: Same as the corresponding steps in the firstembodiment (refer to the description of the first embodiment).

[0160] Step 80: The field current of the motor is reduced compared withthat in the normal condition (that is, when the catalyst is in an activecondition). More specifically, the field current is determined from thecurrent engine rpm or starter rpm by referring to a map.

[0161] Step 90: The state of charge of the battery 10 is checked. If thestate of charge is low (the result of the decision is NO), the fieldcurrent reducing control is stopped, and the process proceeds to step 30to switch to the normal engine control. If the state of charge is high(the result of the decision is YES), the process proceeds to the nextstep 100.

[0162] Step 100: Decision is made as to whether the engine coolanttemperature (or oil temperature) lies within a range not lower than asecond predetermined temperature T1 (for example, −10° C.) and nothigher than a third predetermined temperature T2 (for example, 100° C.).If the result of the decision is NO, that is, if the temperature islower than the second predetermined temperature T1 or higher than thethird predetermined temperature T2, the field current reducing controlis stopped, and the process proceeds to step 30 to switch to the normalengine control. If the result of the decision is YES, the processproceeds to the next step 110.

[0163] Step 110: Decision is made as to whether the engine rpm orstarter rpm is lower than a predetermined rpm M. If the result of thedecision is YES, the field current reducing control is stopped, and theprocess proceeds to step 30 to switch to the normal engine control. Ifthe result of the decision is NO, the process proceeds to the next step120.

[0164] Steps 120 to 170: Same as steps 100 to 150 in the firstembodiment (or steps 100A to 150 in the second embodiment) (refer to thedescription of the first embodiment).

[0165] The present embodiment, when any one of the following conditionsa) to d) is satisfied, stops reducing the field current, and switches tothe normal engine control so that the engine can be cranked properly.

[0166] a) The battery 10 is at low state of charge.

[0167] When the battery 10 is at low state of charge, such as when thevehicle has been left standing for an extended period of time, theoutput of the starter 1 drops. Accordingly, when the battery 10 is atlow state of charge, the field current is not reduced, and the motor isdriven with a high torque type characteristic so that the engine can bestarted properly.

[0168] b) The coolant temperature of the engine is lower than the secondpredetermined temperature T1.

[0169] At extremely low temperatures, the viscosity of the engine oilincreases, requiring higher engine cranking torque when starting theengine. Accordingly, when the coolant temperature or oil temperature ofthe engine is lower than the second predetermined temperature T1 belowwhich higher engine torque is required, the field current is notreduced, and the motor is driven with a high torque type characteristicso that the engine can be driven properly even at extremely lowtemperatures.

[0170] c) The coolant temperature of the engine is higher than the thirdpredetermined temperature T2.

[0171] In high temperature conditions, such as when the engine isstopped after heavy load driving such as uphill driving, and the engineis restarted immediately, the cylinder is sealed more tightly, requiringhigher engine torque when starting the engine. Accordingly, when thecoolant temperature or oil temperature of the engine is higher than thethird predetermined temperature T2 above which a higher engine torque isrequired, the field current is not reduced, and the motor is driven witha high torque type characteristic so that the engine can be drivenproperly even at extremely high temperatures.

[0172] d) Engine rpm is lower than the predetermined rpm M.

[0173] When the engine is driven at high speed by reducing the fieldcurrent of the motor, if the engine rpm does not rise (remains lowerthan the predetermined rpm M) for some fault, the field current is notreduced, and the motor is driven with a high torque type characteristicso that the engine can be driven properly even in a faulty condition.

[0174] In the electrical circuit diagram shown in FIG. 1, batteryvoltage is applied to the energization circuit 5 that controls the fieldcurrent of the shunt coil 6, but alternatively, as shown in FIG. 7, aseparate power supply 12 (power supply means of the present invention)for energizing the shunt coil 6 may be used. This has the merit of beingable to prevent the battery voltage from dropping due to a large currentflow to the armature 3 when controlling the field current of the shuntcoil 6.

[0175] When the separate power supply 12 (for example, a capacitor) isused, if the state of charge of the separate power supply 12 is lowerthan the required level, the magnetic field necessary for driving themotor cannot be formed; in that case, the field current reducing controlis stopped, and the motor is driven with a high torque typecharacteristic so that the engine can be driven properly even in afaulty condition.

[0176] (Embodiment 4)

[0177] This embodiment concerns an example in which field current iscontrolled in a series-wound motor that does not have a shunt coil.

[0178]FIG. 8 is an electrical circuit diagram of an engine startingapparatus B.

[0179] In the engine starting apparatus B of this embodiment, the motorhas two sets of field coils 4 (series coils), and a normally closedrelay 13 (field current reducing means of the present invention) isprovided between the armature 3 and one set of field coils 4 a.

[0180] Here, when a switch 13 b of the normally closed relay 13 is inthe closed condition, both the field coils 4 a and 4 b are energized, sothat the field current increases and the engine can be driven with hightorque. On the other hand, when the switch 13 b is opened by energizinga coil 13 a of the normally closed relay 13 under control of the ECU 2,the field current flows only in the other set of field coils 14 b; as aresult, the field current decreases compared with the case where theswitch 13 b is closed, and the engine can thus be driven at high speed.

[0181] The engine starting apparatus B of this embodiment offers thesame effect as achieved in the first to third embodiments, that is, theemissions (HC) can be reduced by reducing the motor field current anddriving the engine at high speed when the catalyst is in an inactivecondition.

[0182] (Modification)

[0183] The first to fourth embodiments have each dealt with theconfiguration in which the output characteristic of the single starter 1is varied, but alternatively, two starters may be used, the firststarter having a high torque type output characteristic and the secondstarter having a high speed type output characteristic. In this case, byusing the second starter when the catalyst is in an inactive condition,the engine can be cranked at high rpm, as in the first to fourthembodiments. Furthermore, when any one of the conditions to stopreducing the field current, described in the third embodiment issatisfied, the second starter is stopped and the first starter isswitched in to start the engine at high torque; this ensures reliabledriving of the engine.

What is claimed is:
 1. An engine starting apparatus for starting anengine by using at least a starter, comprising a catalyst conditionjudging means for judging whether a catalyst for purifying exhaust gasin the engine is in an inactive condition or not, wherein when startingthe engine, if the catalyst is judged to be in an inactive condition,the engine is started at high speed, compared with the engine speed whenthe catalyst is in an active condition.
 2. An engine starting apparatusas claimed in claim 1, comprising a first starter having a high torquetype output characteristic and a second starter having a high speed typeoutput characteristic, wherein the engine is started at high speed byusing the second starter.
 3. An engine starting apparatus as claimed inclaim 1, wherein said catalyst condition judging means judges that thecatalyst is in an inactive condition when the temperature of thecatalyst is lower than a predetermined temperature.
 4. An enginestarting apparatus as claimed in claim 1, wherein said catalystcondition judging means judges that the catalyst is in an inactivecondition when oil temperature or coolant temperature of the engine islower than a first predetermined temperature.
 5. An engine startingapparatus as claimed in claim 1, wherein said catalyst condition judgingmeans judges that the catalyst is in an inactive condition when theengine has been in a stopped condition for more than a predeterminedlength of time.
 6. An engine starting apparatus as claimed in claim 1,wherein the engine starting apparatus is used in an engine automaticstopping/starting system which automatically controls the stopping andrestarting of said engine, and wherein said catalyst condition judgingmeans judges that the catalyst is in an inactive condition when theengine is started by operating an ignition key but not when the engineis restarted by the engine automatic stopping/starting system.
 7. Anengine starting apparatus as claimed in claim 1, further comprisingmotor control means for controlling an output characteristic of a motorprovided in said starter, and wherein the motor control means controlsthe output characteristic of the motor to a high speed type, therebyallowing the engine to be started at high speed.
 8. An engine startingapparatus as claimed in claim 7, wherein said motor control meanscontrols the output characteristic of the motor to the high speed typeby reducing the field current of the motor.
 9. An engine startingapparatus as claimed in claim 8, wherein said motor has a series coiland a shunt coil, and said motor control means comprises an energizationcircuit which can energize the shunt coil in such a manner that thefield current flowing in the shunt coil is opposite in direction to thefield current flowing in the series coil, and the motor control meansreduces the field current of the motor by controlling, through theenergization circuit, at least either the amount of the current or thedirection of the current flowing in said shunt coil.
 10. An enginestarting apparatus as claimed in claim 8, wherein said motor controlmeans includes a field current reducing means capable of reducing thefield current flowing in a field coil (series coil) of the motor, andthe motor control means reduces the field current of the motor by usingthe field current reducing means.
 11. An engine starting apparatus asclaimed in claim 8, wherein said motor control means reduces the fieldcurrent of the motor in accordance with the number of revolutions of theengine or the starter.
 12. An engine starting apparatus as claimed inclaim 10, wherein said motor control means reduces the field current ofthe motor in accordance with a crankshaft position in the engine.
 13. Anengine starting apparatus as claimed in claim 12, wherein said motorcontrol means reduces the field current of the motor after a pistonreaches the top dead center in any one of cylinders after a start of theengine.
 14. An engine starting apparatus as claimed in claim 8, whereinsaid motor control means sets an electric current value that maximizesthe output of the motor as a control target value for the field current.15. An engine starting apparatus as claimed in claim 8, wherein saidmotor control means stops the field current reducing control when an oiltemperature or a coolant temperature of the engine is lower than asecond predetermined temperature which is lower than the firstpredetermined temperature for judging whether the catalyst is in aninactive condition or not.
 16. An engine starting apparatus as claimedin claim 8, wherein said motor control means stops the field currentreducing control when an oil temperature or a coolant temperature of theengine is higher than a third predetermined temperature which is higherthan the first predetermined temperature for judging whether thecatalyst is in an inactive condition or not.
 17. An engine startingapparatus as claimed in claim 8, wherein said motor control means stopsthe field current reducing control when the speed of the engine or thestarter has failed to reach a predetermined speed.
 18. An enginestarting apparatus as claimed in claim 8, wherein said motor controlmeans stops the field current reducing control when a battery is in alow state of charge.
 19. An engine starting apparatus as claimed inclaim 9, comprising a power supply means for passing a field current tothe shunt coil, separately from a battery, wherein said motor controlmeans stops reducing the field current when the power supply means is atlower state of charge than a predetermined battery charge level.
 20. Anengine starting apparatus as claimed in claim 7, wherein said motorprovided in the starter is a DC motor.
 21. An engine starting apparatusas claimed in claim 2, wherein the engine is started by using the firststarter when an oil temperature or a coolant temperature of the engineis lower than a second predetermined temperature which is lower than thefirst predetermined temperature for judging whether the catalyst is inan inactive condition or not.
 22. An engine starting apparatus asclaimed in claim 2, wherein the engine is started by using the firststarter when oil temperature or coolant temperature of the engine ishigher than a third predetermined temperature which is higher than thefirst predetermined temperature for judging whether the catalyst is inan inactive condition or not.
 23. An engine starting apparatus asclaimed in claim 2, wherein when the engine was started using the secondstarter but, if the speed of the engine or the second starter failed toreach a predetermined speed, the engine is started by switching from thesecond starter to the first starter.
 24. An engine starting apparatus asclaimed in claim 2, wherein the engine is started by using the firststarter when the state of charge of a battery is low.
 25. An enginestarting apparatus as claimed in claim 1, wherein when the engine speedis higher than a predetermined speed, the amount of fuel injection isreduced compared with a case where the catalyst is in an activecondition.
 26. An engine starting apparatus as claimed in claim 25,wherein when the engine speed is higher than the predetermined speed,the amount of fuel injection is reduced depending on air/fuel ratio. 27.An engine starting apparatus as claimed in claim 1, wherein fuelinjection is started after it is detected that an intake manifoldpressure in the engine is lower than a predetermined value.
 28. Anengine starting apparatus as claimed in claim 1, wherein fuel injectionis started after it is detected that the engine speed is higher than apredetermined speed.
 29. An engine starting apparatus as claimed inclaim 1, wherein fuel injection is started after it is detected that thetotal rpm of the engine counted from the starting of the engine hasreached a predetermined value.
 30. An engine starting apparatus asclaimed in claim 1, wherein fuel injection is started after it isdetected that a predetermined time has elapsed from a start of theengine.
 31. An engine starting apparatus as claimed in claim 1, whereinwhen starting the engine by driving the engine at high speed, athreshold speed for perfect combustion is changed according to theengine speed.
 32. An engine starting apparatus as claimed in claim 31,wherein when the engine speed has reached the threshold speed forperfect combustion, operation of the starter is stopped.